1. Field of the Invention
The invention relates to a material handling and stair climbing vehicle that advances as wheels with two or more axles relatively revolve.
2. Description of Related Art
For example, US 2001/0001992 A1 describes a stair climbing vehicle that includes a main body portion capable of travelling with the use of four wheels and a material-carrying portion on which an occupant can ride. Axles of front and rear two wheels are turnably supported by respective ends of an arm, the center of the arm is turnably supported by a lower portion of the main body portion, and the material-carrying portion is turnably supported on an upper portion of the main body portion. In such a configuration, when the stair climbing vehicle climbs stairs, a sequence of actions described below is repeatedly performed. Specifically, the main body portion is turned toward the stairs so that the center of gravity of the stair climbing vehicle is shifted toward the stairs, and the arm is turned around the axle of, for example, each front wheel on the stair side (which means each front wheel in the travelling direction). Then, immediately before each rear wheel (which means each rear wheel in the travelling direction) is grounded on a step surface of a first step of the stairs, the main body portion is turned toward the side opposite from the stair side so that the center of gravity is shifted toward the side opposite from the stair side.
When the above-described stair climbing vehicle climbs the stairs, the center of gravity of the stair climbing vehicle is shifted by a large amount. Therefore, the angle of inclination of the main body portion with respect to the step surfaces of the stairs, the inclination being caused due to the turning of the main body portion, becomes large, and the stair climbing vehicle is likely to be unstable when climbing the stairs. Thus, the climbing speed is restricted, and, further, for example, the main body portion may come into contact with the stairs.